The present invention relates to an improved brake monitoring system, particularly for use on heavy vehicles, such as a tractor and trailer combination, buses and the like, having a spring brake actuator.
Heavy-duty trucks, buses and other large vehicles are typically equipped with a pneumatic brake actuating system. The brake actuating system typically applies air under pressure to a service chamber of a brake actuator to move a diaphragm in a first direction. A push rod typically moves with the diaphragm and the push rod is connected to a linkage which actuates the vehicle brakes. An emergency chamber having a power spring and a second diaphragm is typically mounted on the service chamber and is operable to move the push rod and actuate the brakes in the event that the pneumatic vehicle system fails or when the vehicle is turned off when the vehicle is parked. Thus, the emergency chamber serves as an emergency braking system for the vehicle and a parking brake.
A brake actuator has a predetermined amount of available movement of the push rod or stroke of the push rod. The amount of movement of the push rod required to fully actuate the braking system of the vehicle should be carefully monitored, such that it is within the stroke of the push rod of the brake actuator. Excessive movement of the push rod can be created by one of several factors. Typically, excessive movement of the push rod is due to brake lining wear. As the brakes wear, more movement of the push rod is required to actuate the brakes. Further, as the linkages and connections between the push rod and the linkages, et cetera, bend or become loose or excessively worn, additional push rod movement may be required to actuate the brakes. A combination of these several factors may sometimes cause the amount of push rod movement required to actuate the brakes approach the available push rod movement or stroke available from the brake actuator. As will be understood, this is an undesirable situation.
The prior art has proposed various methods and apparatus to monitor the push rod movement during actuation of the brake and provide some indication to an operator as to when there is excessive push rod movement, which is referred to as xe2x80x9coverstroke.xe2x80x9d As will be understood, a determination of when there is excessive push rod movement or overstroke is dependent upon the designed or rated stroke of the brake actuator. For example, the push rod of a typical brake actuator includes a brightly colored ring, which may be painted on the push rod, which indicates an overstroke condition when the ring extends out of the brake actuator during actuation of the brakes. The ring may, however, be difficult to see because of the location of the brake actuators beneath the truck or trailer and accumulated road debris. Automatic slack adjusters located between the push rod and the foundation brake are also conventionally used, wherein the slack adjuster incrementally adjusts to compensate for slack in the braking system and to decrease the required push rod movement.
The prior art has also proposed various electronic monitoring systems which generally monitor either the stroke of the push rod or the movement of the linkages between the push rod and the foundation brake including the slack adjuster. However, there are several obstacles to be overcome. First, powering and monitoring electronic indicators on each brake actuator of an 18-wheel vehicle is costly. Further, the hostile environment in which the brake actuators are mounted beneath the vehicle can damage the monitoring system, particularly where there are exposed pistons, sleeves, sensors, et cetera. Finally, where the stroke of the push rod is monitored by the brake monitoring system, it is essential that the push rod stroke monitoring system be accurately assembled on the brake actuator and be able to withstand the hostile environment of the brake actuator. Finally, it is desirable that the components of the brake monitoring system be easily and accurately assembled on the brake actuator without special tools.
The present invention relates to an improved brake monitoring system which may include a plurality of brake monitors mounted on each of the plurality of brake actuators of a vehicle. As set forth above, a conventional brake actuator includes a housing having an opening therethrough, a reciprocal rod or push rod extending through the housing opening and typically an annular stone shield mounted within the housing opening surrounding the push rod preventing debris from entering the brake actuator housing.
In the improved brake monitoring system of this invention, an improved elongated annular sleeve is received around the push rod which is fixed relative to the push rod and contains one of the sensor elements. The other sensor element is fixed relative to the brake actuator housing, preferably in the stone shield. The improved annular sleeve in the brake monitoring system of this invention is integrally formed of plastic, including opposed sleeve portions, generally semicircular in cross-section, and a longitudinal integral flexible hinge portion interconnecting the adjacent first sides of the opposed generally semicircular sleeve portions, thereby permitting the sleeve to be molded in one piece and the sleeve portions to be received around the rod following assembly of the brake actuator. In the most preferred embodiment of the sleeve, the opposed sides of the generally semicircular sleeve portions, spaced from the integral flexible hinge portion, include integral connector elements for interconnecting the second sides of the sleeve portions. Thus, the sleeve may be formed as an integral molded plastic part which may be easily and accurately assembled on the push rod. The sleeve assembly further includes an adjustable locking clamp, preferably comprised of identical semicircular plastic components, which permit adjustment of the sleeve on the push rod following assembly and clamping of the sleeve to the push rod. In the disclosed and preferred embodiment, the connector element includes a plurality of opposed spaced male and female connector elements which are integrally formed on the second sides of the sleeve, permanently attaching the second sides of the generally semicircular sleeve portions upon receipt of the sleeve on the rod. The clamp includes a pair of opposed resilient clamping members which surround the rod and the rod preferably includes a grooved portions for receipt of the semicircular resilient clamping members and accurate location of the sleeve relative to the push rod.
In the most preferred embodiment of the vehicle brake monitor of this invention, the sensing element in the sleeve is an elongated bar-shaped magnet and the sensing element in the stone shield is a Hall-effect sensor which may be utilized to continuously monitor the location of the sleeve during actuation of the brake actuator by continuously monitoring the magnetic field of the elongated bar-shaped magnet. In the most preferred embodiment, the magnet has a first longitudinal portion which is magnetized on one face to define a north magnetic field and a second longitudinal portion which is magnetized on an adjacent face to define a south magnetic field. The most preferred magnet is a ceramic magnet able to withstand the adverse temperature conditions experienced by brake actuators, wherein the faces of the first and second portions opposite the sensor in the stone shield are magnetized as set forth above. As set forth below, a brake monitoring system having a magnet as described and a sensor in the stone shield may be utilized to monitor an overstroke condition, wherein the push rod extends out of the brake actuator housing beyond the rated stroke indicating wear of the foundation brake or misalignment or wear of the linkages described above, a dragging brake condition, wherein the push rod does not fully retract into the brake actuator, a normal stroke condition and a nonfunctioning brake actuator.
As will be understood, it is necessary to maintain the orientation of the sensing element in the stone shield opposite the sensing element in the sleeve in the improved vehicle brake monitoring system of this invention. This is accomplished in the vehicle brake monitoring system of this invention by providing a keyway slot in the stone shield and an elongated longitudinally extending radial key on the sleeve which is slideably received in the keyway in the stone shield, thereby maintaining the orientation of the sleeve relative to the stone shield during actuation of the brake. The vehicle brake monitoring system of this invention is thus easy to assemble accurately on the brake actuator and the brake actuator push rod stroke monitoring system of this invention is rugged and able to withstand the adverse conditions encountered by the brake actuator. Other advantages and meritorious features of the vehicle brake monitoring system of this invention will be more fully understood from the following description of the preferred embodiments, the claims and the appended drawings, a brief description of which follows.